This invention relates to a drop pin for stop motion comprising a body with a yarn lead-through opening provided to rest on a thread extending through this opening by means of a supporting edge bordering this opening.
Known drop pin for stop motion is carried out as an elongated, mainly flat metal element with a limited thickness. The drop pin has an upper part in which an elongated slot extending in the longitudinal direction of the drop pin has been provided. The drop pin has a lower part with two equally long legs which extend in the longitudinal direction of the drop pin, at a small intermediate distance, parallel to each other and which, with their extremities, form the lower end of the drop pin. The slot and the gap provided between said legs are separated from each other by a narrow intermediate strip.
The gap ends at the top in an opening that, along the top, is bordered by the flat lower edge of said intermediate strip. This opening has been provided to lead through a warp thread and is called in the patent application the yarn lead-through opening. The parts of the drop pin extending on both sides of this opening are cambered in the opposite direction perpendicular to the surface of the drop pin, so that a thread extending through this opening may extend in the plane of the drop pin.
During weaving, drop pins for stop motion are used on a weaving machine as a means of detection to detect a thread breakage. For that purpose each warp thread on the weaving machine is lead through the yarn lead-through eye of a respective drop pin for stop motion, so that the drop pin is supported by the tightened warp threads. Besides, each warp thread extends in the plane of the drop pin, so that the drop pins take up only little space as to width and the warp threads may be running very close to each other. On a weaving machine there are a great number of drop pins for stop motion next to each other in a working position, being carried by the warp threads running close together next to each other. In case a warp thread breaks, the drop pin falls down into a position where it can be detected by the detection means. This is, for instance, realized in that the drop pin in its lowered position causes an electric contact. In consequence of the detection that the warp thread has left its working position, a signal is generated, as a result of which a warning is given for instance and/or the machine is brought to a standstill automatically.
During weaving the drop pins for stop motion are kept in their positions and the warp thread is moving through the yarn lead-through opening. With the upper edge of the yarn lead-through opening, the drop pins rest on their respective warp thread and during weaving the thread moving forward is sliding over this surface. In this patent application the surface of the drop pin with which the drop pin rests on the warp thread is called the supporting edge. With these known drop pins for stop motion the supporting edge is formed by the flat lower edge of said strip. This edge forms a straight upper limitation of the yarn lead-through opening, running perpendicular to the longitudinal axis of the drop pin in the plane of the drop pin.
A drop pin for stop motion of the type described above is describes in the German Gebrauchsmuster-publication DE 299 20 333U1.
When using these drop pins for stop motion in thread breakage detection devices for weaving machines it is found that the warp threads experience a relatively strong resistance when led through the drop pins for stop motion. A fairly large number of hitches of the warp threads moving forward is also found, and this mainly when weaving with relatively thick and/or coarse yarns. These hitches cause thread breakages and/or machine stops and reduce the productivity of the weaving machine.
In GB 407.514 a drop pin for stop motion is described, the supporting edge of which, bordering the lead-through opening along the top, has a curved course in the plane of the drop pin.
Yet, with these drop pins the disadvantages mentioned above are still found.
The objective of this invention is to provide for an improved type of drop pin for stop motion, with which the above-mentioned disadvantages may be remedied or considerably reduced.
According to the invention, this objective is achieved by providing a drop pin for stop motion with the characteristics mentioned in the first paragraph of this description, said supporting edge, according to this invention, having a convex shape in cross-section.
With this, all sharp angles of the trajectory of the thread are avoided. With the known drop pins the flat or curved supporting surface in the lead-through opening forms a right angle with the two flanks of the drop pin. Thickenings, notches or protruding fibers of the warp threads are easily caught by these right angles. With the drop pin according to the invention all right or sharp angles are avoided.
In the sense of this patent application, a convex form may mean a projecting spherical form as well as a projecting form existing of several angle forming connecting sides (such as for instance a polygon). In the first situation the thread will, of course, not encounter any angles, whereas in the second situation all angles encountered by the thread during its passing the drop pin, are obtuse angles. In both cases it is found that hitches of the warp threads are considerably less frequent.
This measure has led to a particularly remarkable reduction of the disadvantages of the known drop pins described above.
Preferably, these improved drop pins for stop motion are carried out with a supporting surface forming an evenly curved bordering of the yarn lead-through opening. Because of this the risk of warp threads getting stuck is still further reduced. However, the most preferred drop pin for stop motion according to this invention has a supporting surface that forms a mainly circular bordering of the yarn lead-through opening.
The form of the supporting surface seen in a cross-section may be a rounded spherical form as well as a form with a number of angle forming sides, such as for instance the form of a polygon. The advantageous effect of this embodiment has been indicated above in this description.
It is best, to carry out the edge, bordering the yarn lead-through opening, over almost its entire length as the supporting surface. This means that almost the entire bordering of the lead-through opening is curved concavely, and the cross-section of which shows a convex form such as described above for the supporting edge. Preferably, this entire bordering of the yarn lead-through opening is circular.
Ideally, this drop pin is also carried out in such a way, that the parts of the drop pin for stop motion, bordering the yarn lead-through opening on both sides of the longitudinal axis of the drop pin, are removed from each other in a direction perpendicular to the surface of the drop pin, so that a thread extending through the yarn lead-through opening may extend in the plane of the drop pin for stop motion.
Also a device for detecting thread breakages on a weaving machine, comprising a number of drop pins for stop motion according to this invention, as well as a weaving machine provided with a similar device are within the scope of this invention.
In the following description a preferred embodiment of a drop pin for stop motion according to the invention is described in more details. The only purpose of this description is to further clarify the invention. Consequently nothing in this description may be considered as being a ground for a limiting interpretation of the scope of protection defined in the claims. In this description reference is made to the attached figures, where